[Amps] Pre-heating of tubes

[Will Matney]

Guillermo,

It's impossible for the getter to absorb gas unless the anode is heated up hot enough to do it, if that's where the getter is at. I read some have two filaments of zirconium made to heat up to two different temperatures. The high heat one to absorb, O2, CO2, etc, and the lower heated one to absorb the hydrogen the hotter one emitted. If it's tantalum, you don't have to heat it up as hot, nor have two different temperatures. The temperature on it though runs around 1000 deg C (red-orange hot) for optimum absorption. If it is the anode type, the anode has to be heated red orange for tantalum, and yellow to white hot for zirconium just to absorb the gas properly. Under 300 deg C which is just under where you can't see the anode turn red in the dark, is where zirconium will not do any good at all, neither for hydrogen or O2 and the others. These heat colors work for any metal, but not for graphite. You can check them against any heat treatment or metalurgical chart.

In running the heater only, if the heater isn't coated in something to absorb gas which it shouldn't be, can liberate a slight amount of gas into the tube where it gets as hot as it is. The only way to get the anode up to the correct temperature then for an anode type getter would be to apply anode voltage so the anode will heat up.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 7/29/06 at 12:49 AM GGLL wrote:

>Ian White GM3SEK escribió:
>
>> 
>> It also explains why transmitting tubes generally need to be pre-heated 
>> after a long period out of use. The process of slow diffusion to the 
>> surface of the materials means that gas will probably have accumulated, 
>> and the getter needs some time at a high temperature in order to do its 
>> job.
>
>	Very clear explanation, Ian, thank you very much. I want to ask something
>about.
>	This pre-heating process (in, for example, NOS tubes or those used in
>good 
>condition but long time stored ones) must also be done by making the anode 
>orange hot in high power tubes (those with "gettered" anodes) or it's just 
>enough to run them with filament on for many hours?.
>
>
>Best regards
>Guillermo - LU8EYW.
>
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